1. Field of the Invention
The present invention generally relates to a cooling fan and an assembly method thereof and, more particularly, to a cooling fan having a metal seat and a circuit board easily mounted on the metal seat while insulation between the circuit board and the metal seat is ensured, as well as to an assembly method of the cooling fan.
2. Description of the Related Art
FIG. 1 shows an engagement structure of a stator unit of a cooling fan disclosed in Taiwan Patent No. M387164. The cooling fan 8 includes a housing 81, a stator unit 82 and a blade unit 83. The housing 81 forms a seat 811 and a shaft tube 812 by integral injection. The seat 811 has a plurality of first engaging portions 813. The stator unit 82 has a stator 821 consisting of a plurality of stacked coils and silicon steel plates. The stator 821 is coupled with a circuit board 822 and includes a plurality of second engaging portions 823.
In assembly, the circuit board 822 is coupled to the bottom face of the stator 821 by forcing the second engaging portions 823 of the stator 821 through the holes of the circuit board 822. The stator 821 is then mounted on the seat 811 by forcing the shaft tube 812 through the circuit board 822 and the stator 821. Next, the first engaging portions 813 and the second engaging portions 823 are engaged with each other. Finally, the blade unit 83 is coupled with the shaft tube 812 to complete the assembly procedure of the cooling fan 8.
However, the height of the cooling fan 8 cannot be reduced due to the arrangements of the first engaging portions 813 and the second engaging portions 823. As a result, it is difficult to miniaturize the cooling fan 8. Furthermore, it is inconvenient to assemble the cooling fan 8 due to the steps of coupling the circuit board 822 with the stator unit 82 and engaging the second engaging portions 823 with the first engaging portions 813. Moreover, the first engaging portions 813 or the second engaging portions 823 could break during the assembly procedure, affecting the engagement between the seat 811 and the stator unit 82. Still further, since the housing 81 is made of plastic, certain parts of the seat 811 (such as ribs) are fragile. Consequently, the structural strength of the cooling fan 8 is low, and the quality of the cooling fan 8 is poor.
To solve the problem, Taiwan Patent No. 1353509 discloses a fan casing structure as shown in FIG. 2. The fan casing 9 includes a support board 91. The support board 91 includes a bottom plate 911 and a shaft tube portion 912 located at the center of the bottom plate 911. The support board 91 may be mounted with certain components, such as a stator unit, a blade unit or the like, to construct a cooling fan.
Although the bottom plate 911 of the fan casing 9 has higher strength and quality, it is still inconvenient to assemble a cooling fan using the fan casing 9 and is still difficult to reduce the height of the cooling fan, as it is the case of the cooling fan 8. This is because it is inconvenient to form the stator unit by assembling the silicon steel plates, the coils and the circuit board before the stator unit can be installed in the fan casing 9 (the coils and the circuit board are essential components to the stator unit, as can be readily appreciated by one skilled in the art). More importantly, it is also difficult to ensure satisfactory insulation between the circuit board and the bottom plate 911, since the bottom plate 911 is made of metal.